Display element, polarizing plate, and display apparatus and projecting apparatus using the display element and polarizing plate

ABSTRACT

This invention provides a liquid crystal display apparatus which can reduce thermal load on a polarizing plate or display element, decrease the number of components necessary for reducing the thermal load on the polarizing plate, and reduce cost by decreasing the power consumption of a cooling fan. The display apparatus has a unit for changing the color purity of at least one of a puerility of colors. A polarizing plate in the optical path of light whose color purity is changed by the color purity changing unit is formed from a heat-transfer transparent substrate having a thermal conductivity of 1.2 W/(m·K) or more.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a display apparatus and aprojecting apparatus used to display, e.g., a computer image or videoimage on a large screen.

[0003] 2. Related Background Art

[0004] In recent years, demand has arisen for a projection-type displayapparatus with improved brightness. FIG. 15 shows the arrangement of aconventional projection-type display apparatus. Referring to FIG. 15,white light emitted from a light source section 1 passes through fly-eyelenses 3 and 4, PS conversion element 5, and condenser lens 6. Adichroic mirror DM1 transmits a red-band light component and reflectsgreen- and blue-band light components. As the light source, generally, ahalogen lamp, metal halide lamp, ultrahigh-pressure mercury-vapor lamp,or the like is used. As a color separation/synthesis optical element, adichroic mirror, dichroic prism, or the like is used.

[0005] The red-band light component transmitted through the dichroicmirror DM1 that exhibits a spectral transmittance shown in FIG. 16Achanges its optical path by 90° at a total-reflecting mirror M1, strikesa liquid crystal display element 8R through a field lens 7R and atrimming filter TR that exhibits a spectral transmittance shown in FIG.16C, and is optically modulated here in accordance with the inputsignal. The optically modulated light component becomes incident on adichroic prism 9, changes its optical path by 90° at the dichroic prism9, and strikes a projecting lens 10.

[0006] On the other band, the green- and blue-band light componentsreflected by the dichroic mirror DM1 to change the optical paths by 90°become incident on a dichroic mirror DM2 that exhibits a spectraltransmittance shown in FIG. 16B. As is apparent from FIG. 16B, since thedichroic mirror DM2 has a characteristic for reflecting the green-bandlight component, the green-band light component is reflected to changeits optical path by 90°, becomes incident on a liquid crystal displayelement 8G through a field lens 7G and a trimming filter TG thatexhibits a spectral transmittance shown in FIG. 16D, and is opticallymodulated here in accordance with the input signal. The opticallymodulated green-band light component strikes the dichroic prism 9 andprojecting lens 10 in this order.

[0007] The blue-band light component transmitted through the dichroicmirror DM2 becomes incident on a liquid crystal display element 8Bthrough a condenser lens 11, relay lens 12, total-reflecting mirrors M2and M3, and field lens 7B, and is optically modulated here in accordancewith the input signal. The optically modulated blue-band light componentstrikes the dichroic prism 9 to change its optical path by 90° at thedichroic prism 9, and then strikes the projecting lens 10.

[0008] In the conventional projection-type display apparatus having theabove arrangement, polarizing plates necessary before and after theliquid crystal display element 8 are stuck to a transparent glass membersuch as the protective glass member used for the liquid crystal displayelement 8, the field lens 7, or the dichroic prism 9.

[0009] When the aperture ratio of the liquid crystal display element islow, and the light quantity of the lamp used is small, a transparentglass substrate (thermal conductivity: about 1 W/(m·K)) suffices, as inthe prior art.

[0010] The brightness of a screen is recently improved by using a1.3-type liquid crystal display element having about 770,000 pixels andan aperture ratio of 60% or increasing the power consumption of thelamp. Additionally, liquid crystal display elements are becomingcompact.

[0011] However, this increases the thermal load on the polarizing platenecessary for the liquid crystal display element, posing another problemof degradation in performance of the polarizing plate.

[0012] In addition, when display with priority on the brightness anddisplay with priority on the color reproducibility are realized by asingle apparatus, as disclosed in Japanese Patent Application Laid-OpenNo. 7-72450, the polarizing plate has larger thermal load becausedisplay with priority on the brightness uses a wavelength region (about570 to 600 nm) that is not used for display with priority on the colorreproducibility.

[0013] To solve the thermal load on the polarizing plate, sapphire (42W/(m·K)) having a thermal conductivity about 40 times that of atransparent glass substrate is used as the substrate of the polarizingplate, as disclosed in Japanese Patent Application Laid-Open No.11-231277. However, if the problem of thermal load is solved simplyusing sapphire, a 3-CCD projection-type display apparatus as shown inFIG. 15 or a projection-type display apparatus that realizes, by asingle apparatus, display with priority on the brightness and displaywith priority on the color reproducibility, as disclosed in JapanesePatent Application Laid-Open No. 11-231277, requires a total of sixsapphire substrates, resulting in large increase in cost.

[0014] When the cooling efficiency is increased using a cooling fan, thepower consumption of the cooling fan increases. Especially, when displaywith priority on the brightness and display with priority on the colorreproducibility are realized by a single apparatus, as disclosed inJapanese Patent Application Laid-Open No. 7-72450, it is not preferablebecause cooling must be set in consideration of display with priority onthe brightness, where the light quantity increases, while cooling iswasteful for display with priority on the color reproducibility.

[0015] The power consumption of the cooling fan may be changed betweendisplay with priority on the brightness and display with priority on thecolor reproducibility. However, a system for switching the powerconsumption must be incorporated, resulting in an increase in cost orspace.

SUMMARY OF THE INVENTION

[0016] It is therefore an object of the present invention to provide adisplay apparatus which has a means for changing the color purity of atleast one of a plurality of color light components, in changing thecolor purity of at least one color light component, can reduce thethermal load on the polarizing plate, and can reduce the cost bydecreasing the power consumption of a cooling fan.

[0017] In one aspect of the invention, a display apparatus for forming acolor image by illuminating one or a plurality of display elements withlight from a light source and modulating a plurality of color lightcomponents having different colors by the display elements, comprisesmeans for changing a color purity of at least one of the plurality ofcolor light components, and a polarizing plate in an optical path of thelight component whose color purity is changed by said color puritychanging means, wherein said polarizing plate has a transparentsubstrate including a material having a thermal conductivity higher than2 W/(m·K).

[0018] In another aspect of the invention, said color purity changingmeans can adjust whether a light component in a specific wavelengthregion reaches the display element.

[0019] In another aspect of the invention, the light source has a peakat a certain wavelength of the specific wavelength region.

[0020] In another aspect of the invention, the certain wavelength is 570to 600 nm.

[0021] In another aspect of the invention, the light source comprises ahigh-pressure mercury-vapor lamp, and the certain wavelength is about580 nm.

[0022] In another aspect of the invention, said color purity changingmeans comprises a dichroic mirror.

[0023] In another aspect of the invention, the transparent substrate isessentially made of one of sapphire and fluorite.

[0024] In another aspect of the invention, the transparent substrateincludes a material having a thermal conductivity higher than 5 W/(m·K).

[0025] In another aspect of the invention, the transparent substrate isessentially made of a material having a thermal conductivity higher than2 W/(m·K).

[0026] In another aspect of the invention, the display apparatus furthercomprises a plurality of dichroic mirrors for separating white lightfrom the light source into the plurality of color light componentshaving different colors.

[0027] In another aspect of the invention, the display apparatus furthercomprises a plurality of image elements arranged in correspondence withthe plurality of color light components having different colors, and aplurality of dichroic mirrors for combining image light components fromthe plurality of display elements.

[0028] In another aspect of the invention, the display apparatus furthercomprises a plurality of display elements arranged in correspondencewith the plurality of color light components having different colors,and a dichroic prism for combining image light components from theplurality of display elements for modulating the plurality of colorlight components.

[0029] In another aspect of the invention, said dichroic prism is formedby bonding four prisms using an adhesive to have wavelengthselection/reflection layers substantially perpendicular to each other.

[0030] In another aspect of the invention, said color purity changingmeans inserts/removes an optical element to/from an optical path of atleast one of the plurality of color light components or changes aposture of the optical element.

[0031] A projecting apparatus according to one aspect of the inventioncomprises the display apparatus set out in the foregoing, and aprojection system for enlarging and projecting an image formed by thedisplay apparatus.

[0032] In another aspect of the invention, a display apparatus forforming a color image by illuminating one or a plurality of displayelements with light from a light source and modulating a plurality ofcolor light components having different colors by the display elements,comprises means for changing a color purity of at least one of theplurality of color light components, wherein one of the one or pluralityof display elements is in an optical path of the light component whosecolor purity is changed by said color purity changing means, and saidone display element has a transparent substrate essentially made of amaterial having a thermal conductivity higher than 2 W/(m·K).

[0033] In another aspect of the invention, a display apparatus comprisesa light source, one or a plurality of display elements illuminated withlight from said light source, said display elements forming an image bymodulating a plurality of color light components having differentcolors, and one or a plurality of polarizing plates arranged in anoptical path of the light from said light source to equalize polarizingdirections of the light components, wherein at least one of said one orthe plurality of polarizing plates has a transparent substrateessentially formed from a fluorite.

[0034] In another aspect of the invention, the foregoing apparatusfurther comprises means for changing a color purity of at least one ofthe plurality of color light components by inserting/removing an opticalelement to/from an optical path of said at least one color lightcomponent or changing a posture of the optical element in the opticalpath of said at least one color light component.

[0035] In another aspect of the invention, said color purity changingmeans can adjust whether a light component in a specific wavelengthregion reaches the display element.

[0036] In another aspect of the invention, the light source has a peakat a certain wavelength of the specific wavelength region.

[0037] In another aspect of the invention, the certain wavelength is 570to 600 nm.

[0038] In another aspect of the invention, the light source comprises ahigh-pressure mercury-vapor lamp, and the certain wavelength is about580 nm.

[0039] In another aspect of the invention, said color purity changingmeans comprises a dichroic mirror.

[0040] In another aspect of the invention, the transparent substrateincludes a material having a thermal conductivity higher than 5 W/(m·K).

[0041] In another aspect of the invention, the transparent substrate isessentially made of a material having a thermal conductivity higher than2 W/(m·K).

[0042] In another aspect of the invention, the foregoing apparatusfurther comprises a plurality of dichroic mirrors for separating whitelight from the light source into the plurality of color light componentshaving different colors.

[0043] In another aspect of the invention, the foregoing apparatusfurther comprises a plurality of image elements arranged incorrespondence with the plurality of color light components havingdifferent colors, and a plurality of dichroic mirrors for combiningimage light components from the plurality of display elements.

[0044] In another aspect of the invention, the foregoing apparatusfurther comprises a plurality of display elements arranged incorrespondence with the plurality of color light components havingdifferent colors, and a dichroic prism for combining image lightcomponents from the plurality of display elements for modulating theplurality of color light components.

[0045] In another aspect of the invention, said dichroic prism is formedby bonding four prisms using an adhesive to have wavelengthselection/reflection layers substantially perpendicular to each other.

[0046] In another aspect of the invention, a projecting apparatuscomprises the foregoing display apparatus and a projection system forenlarging and projecting an image formed by said display apparatus.

[0047] In another aspect of the invention, a display apparatus comprisesa light source, one or a plurality of display elements illuminated withlight from said light source, said display elements forming an image bymodulating a plurality of color light components having differentcolors, wherein at least one of said one or said plurality of displayelements having a transparent substrate is essentially formed from afluorite.

[0048] In another aspect of the invention, the foregoing apparatusfurther comprises means for changing a color purity of at least one ofthe plurality of color light components by inserting/removing an opticalelement to/from an optical path of the at least one color lightcomponent or changing a posture of the optical element in the opticalpath of the at least one color light component.

[0049] In another aspect of the invention, said color purity changingmeans can adjust whether a light component in a specific wavelengthregion reaches the display element.

[0050] In another aspect of the invention, the light source has a peakat a certain wavelength of the specific wavelength region.

[0051] In another aspect of the invention, the certain wavelength is 570to 600 nm.

[0052] In another aspect of the invention, the light source comprises ahigh-pressure mercury-vapor lamp, and the certain wavelength is about580 nm.

[0053] In another aspect of the invention, said color purity changingmeans comprises a dichroic mirror.

[0054] In another aspect of the invention, the transparent substrateincludes a material having a thermal conductivity higher than 5 W/(m·K).

[0055] In another aspect of the invention, the transparent substrate isessentially made of a material having a thermal conductivity higher than2 W/(m·K).

[0056] In another aspect of the invention, the foregoing apparatusfurther comprises a plurality of dichroic mirrors for separating whitelight from the light source into the plurality of color light componentshaving different colors.

[0057] In another aspect of the invention, the foregoing apparatusfurther comprises a plurality of image elements arranged incorrespondence with the plurality of color light components havingdifferent colors, and a plurality of dichroic mirrors for combiningimage light components from the plurality of display elements.

[0058] In another aspect of the invention, the foregoing apparatusfurther comprises a plurality of display elements arranged incorrespondence with the plurality of color light components havingdifferent colors, and

[0059] a dichroic prism for combining image light components from theplurality of display elements for modulating the plurality of colorlight components.

[0060] In another aspect of the invention, said dichroic prism is formedby bonding four prisms using an adhesive to have wavelengthselection/reflection layers substantially perpendicular to each other.

[0061] In another aspect of the invention, a projecting apparatuscomprises the foregoing display apparatus and a projection system forenlarging and projecting an image formed by said display apparatus.

[0062] In another aspect of the invention, a display element comprises atransparent substrate essentially formed from fluorite, and a drivingsection formed on said substrate.

[0063] In another aspect of the invention, a polarizing plate forequalizing polarizing directions of incident light components andoutputting the light components, comprises a transparent substrateessentially formed from fluorite and a polarizing film formed on saidsubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0064]FIG. 1 is a view showing the arrangement of a projecting apparatusaccording to the first embodiment;

[0065]FIG. 2 is a graph showing the wavelength spectral characteristicof an optical element 13 according to the first embodiment;

[0066]FIGS. 3A and 3B are graphs showing the wavelength spectralcharacteristics of dichroic mirrors according to the first embodiment;

[0067]FIGS. 4A and 4B are graphs showing spectrum distributions instates upon and without insertion of the optical element 13 according tothe first embodiment;

[0068]FIG. 5 is a view showing the operation direction (vertical) of theoptical element 13 according to the first embodiment;

[0069]FIG. 6 is a view showing the operation direction (arc) of theoptical element 13 according to the first embodiment;

[0070]FIG. 7 is a view showing the arrangement when an optical elementis placed in a green wavelength optical path in the second embodiment;

[0071]FIGS. 8A, 8B, and 8C are graphs showing the wavelength spectralcharacteristics of dichroic mirrors and optical element 13 according tothe second embodiment;

[0072]FIGS. 9A and 9B are graphs showing spectrum distributions instates upon and without insertion of the optical element 13 according tothe second embodiment;

[0073]FIG. 10 is a view showing the arrangement using only one liquidcrystal display element according to the third embodiment;

[0074]FIGS. 11A, 11B, 11C and 11D are graphs showing the wavelengthspectral characteristics of the dichroic mirrors according to the thirdembodiment;

[0075]FIG. 12 is a schematic view of an optical path according to thethird embodiment;

[0076]FIG. 13 is a view showing the internal structure and optical pathsin a liquid crystal display element;

[0077]FIG. 14 is a view showing the positional relationship betweencolor band light components and pixels of the liquid crystal displayelement according to the third embodiment;

[0078]FIG. 15 is a view showing the arrangement of a conventionalprojection-type display apparatus;

[0079]FIGS. 16A, 16B, 16C and 16D are graphs showing the wavelengthspectral characteristics of dichroic mirrors and trimming filters of theconventional projection-type display apparatus; and

[0080]FIG. 17 is a view showing the arrangement of a projectingapparatus using a sapphire substrate according to the first embodimentas a display element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0081] The embodiments will be described next in detail in accordancewith the accompanying drawings. In these embodiments, an optical elementhaving characteristics for transmitting a region of a certain wavelengthor more and inhibiting a region of the wavelength or less, or vice versais placed in the optical path, and a mechanism for inserting/removingthe optical element is prepared, thereby realizing display with priorityon the brightness and display with priority on the color reproducibilityby a single projecting apparatus.

[0082] In addition, when the substrate of a display element orpolarizing plate is formed from a material having a thermal conductivityhigher than that of transparent glass (thermal conductivity: about 1W/(m·K)) often used as the substrate of a display element or polarizingplate, e.g., sapphire having a thermal conductivity of about 42 W/(m·K)or fluorite having a thermal conductivity of about 10 W/(m·K), thethermal load on the polarizing plate or display element in display withpriority on the brightness can be relaxed. Furthermore, when a displayelement or polarizing plate formed from a transparent heat-transfersubstrate having a thermal conductivity (thermal conductivity: 2 W/(m·K)or more) higher than that of the transparent glass is used as thesubstrate of a display element in the optical path where the opticalelement is inserted or removed or a polarizing plate before or after thedisplay element, and a display element or polarizing plate formed fromtransparent glass is used in the remaining optical paths, the number ofexpensive heat-transfer transparent substrates can be decreased toreduce the cost. Note that a more satisfactory effect can be obtainedwhen a transparent heat-transfer substrate having a thermal conductivityof 5 W/(m·K) or more, that is obviously higher than that of thetransparent glass (thermal conductivity: 1 W/(m·K)), is used as thesubstrate of a display element or polarizing plate.

[0083] In all embodiments, sapphire having a high thermal conductivityis used as the substrate of a polarizing plate with display with thermalload. However, the present invention is not limited to this, andfluorite may be used in place of sapphire, or any other materials havinghigh thermal conductivities can be used. The sapphire may be used not asthe substrate of a polarizing plate but as the substrate of a displayelement. Other members with large thermal load may also be formed fromsapphire or fluorite. Also, instead of forming the substrate from asingle material such as sapphire or fluorite, the substrate can be madeof a plurality of materials including transparent glass (thermalconductivity: 1 W/(m·K)) as long as at least one of the plurality ofmaterials has a high thermal conductivity.

[0084] [First Embodiment]

[0085]FIG. 1 shows the detailed arrangement of a projection-type displayapparatus according to the first embodiment of the present invention.FIG. 2 shows the spectral transmittance of an optical element 13 used inthis embodiment. FIGS. 3A and 3B show the spectral transmittances ofdichroic mirrors DM1 and DM2 in the above arrangement. These spectraltransmittances are design examples when a certain ultrahigh-pressuremercury-vapor lamp is used. These numerical values are merely examplesand are not limited to these values. Various values can be set inaccordance with the type of light source.

[0086] A red-band light component transmitted through the dichroicmirror DM1 that exhibits the spectral transmittance shown in FIG. 3Achanges its optical path at a total-reflecting mirror M1 by 90° andpasses through a field lens 7R. When the optical element 13 is insertedinto the optical path, the red-band light component passes through theoptical element 13, becomes incident on a sapphire polarizing plate R1and liquid crystal display element 8R, and is optically modulated herein accordance with the input signal.

[0087] The optically modulated light component strikes a sapphirepolarizing plate R2 and dichroic prism 9 in this order, changes itsoptical path by 90° at the dichroic prism 9, and enters a projectinglens 10. When the optical element 13 is not present in the optical path,the light component becomes incident on the liquid crystal displayelement 8R without intervening the optical element 13 and is opticallymodulated here in accordance with the input signal. The opticallymodulated light component becomes incident on the dichroic prism 9,changes its optical path by 90° at the dichroic prism 9, and enters theprojecting lens 10. The dichroic prism 9 here is designed by bondingfour prisms using an adhesive such that the wavelengthselection/reflection layers form an almost cross shape.

[0088] On the other hand, green- and blue-band light componentsreflected by the dichroic mirror DM1 to change the optical paths by 90°strike the dichroic mirror DM2 that exhibits the spectral transmittanceshown in FIG. 3B. As is apparent from FIG. 3B, since the dichroic mirrorDM2 has a characteristic for reflecting green band light G, thegreen-band light component is reflected to change its optical path by90°, becomes incident on a liquid crystal display element 8G through afield lens 7G, and is optically modulated here in accordance with theinput signal. The optically modulated green-band light component strikesthe dichroic prism 9 and projecting lens 10 in this order.

[0089] The blue-band light component transmitted through the dichroicmirror DM2 becomes incident on a liquid crystal display element 8Bthrough a condenser lens 11, relay lens 12, total-reflecting mirrors M2and M3, and field lens 7B, and is optically modulated here in accordancewith the input signal. The optically modulated blue-band light componentstrikes the dichroic prism 9 to change its optical path by 90° at thedichroic prism 9, and then strikes the projecting lens 10.

[0090] When the optical element 13 is not inserted into the irradiationoptical path, although the color purity determined by the cut wavelengthof the dichroic mirrors DM1 and DM2 is lower than the color puritynecessary for natural image display, the display is bright, so a colorpurity sufficient for presentation in, e.g., an office or school is set.When the optical element 13 is not inserted into the irradiation opticalpath, a light component in a band of about 570 to 600 nm is also used asprojection light.

[0091] Conversely, when high-quality display with high color purity isnecessary for natural image display or the like, the optical element 13is inserted into the irradiation optical path. When the optical element13 is inserted into the irradiation optical path, a light component inthe band of about 570 to 600 nm does not emerge to the liquid crystaldisplay element side. Instead, a light component in a band of about 510to 570 nm is used as a green-band display light component, andprojection light of about 600 nm or more is used as a red-band displaylight component.

[0092]FIGS. 4A and 4B show the spectrum characteristics in states uponand without insertion of the optical element 13. When the opticalelement 13 is inserted into the irradiation optical path, and a lightcomponent in the band of 570 to 600 nm is not used, the color purity canimprove. Generally, however, when a light component that lowers thecolor purity is shielded, the light quantity decreases, although thecolor purity improves. For the optical element 13, the cut band andtransmittance are set such that the color purity and color balance canbe ensured without greatly decreasing the light quantity.

[0093] In the arrangement shown in FIG. 1, only the light component inthe red wavelength region changes its light quantity, as shown in FIGS.4A and 4B. Hence, transparent glass is used as the substrates of thepolarizing plates in the blue and green wavelength regions, cooling by acooing fan is done mainly for the blue and green wavelength regions, andsapphire is used as the substrate of the polarizing plate in the redwavelength region where the light quantity changes, the thermal load onthe polarizing plates in the respective wavelength regions can berelaxed. In addition, since the number of sapphire substrates decreases,the cost can be reduced. Furthermore, since cooling by the cooling fanneed only be mainly done for the blue and green wavelength regions wherethe light quantity does not change, the power consumption and size ofthe fan can reduced, and the problem of noise is also relaxed.

[0094] Referring to FIG. 1, the optical element 13 is placed immediatelybefore the liquid crystal display element in the red wavelength opticalpath. However, the optical element 13 can be placed at any positionbetween the dichroic mirror DM1 and the liquid crystal display elementin the red wavelength optical path. Referring to FIG. 1, the opticalelement is moved horizontally. However, the optical element may be movedvertically as shown in FIG. 5 or circularly moved about a certain pointas shown in FIG. 6 to be inserted/removed into/from the optical path.The operation directions of the optical element 13 are not limited tothese directions. Instead of inserting/removing the optical element 13,it may be operated to make an angle with respect to the optical axisusing the fact that the cut wavelength of the dichroic mirror is shiftedto the short wavelength side when the light incident angle is increased.

[0095] The spectral wavelength characteristics of the dichroic mirrorDM1 are not limited to these characteristics. A plurality of opticalelements may be used in accordance with the characteristics.

[0096] Referring to FIG. 1, two sapphire substrates are used as thesubstrates of polarizing plates. However, the number of substrates isnot limited to two. In addition, not sapphire but another material suchas fluorite having a high thermal conductivity may be used. Furthermore,as shown in FIG. 17, instead of using a substrate 100 formed from amaterial such as sapphire or fluorite having a high thermal conductivityas the substrate of a polarizing plate, the substrate may be integratedwith a display element. In this case, sapphire or fluorite can be usedfor both of the substrate of a polarizing plate and the display elementor selectively used for only an optimum one of the polarizing plate anddisplay element.

[0097] [Second Embodiment]

[0098]FIG. 7 shows the detailed arrangement of a projection-type displayapparatus according to the second embodiment of the present invention.When the wavelength spectral characteristic of a dichroic mirror DM1 ischanged to that shown in FIG. 8A, and the wavelength spectralcharacteristic of a dichroic mirror DM2 is changed to that shown in FIG.8B, an optical element 13 having a wavelength spectral characteristicshown in FIG. 8C can be set immediately before the dichroic prism in thegreen wavelength optical path. This optical element 13 can also be setat any position between the dichroic mirror DM1 and the liquid crystaldisplay element in the green wavelength optical path.

[0099]FIGS. 9A and 9B show spectrum characteristics in states upon andwithout insertion of the optical element 13. When the optical element 13is inserted into the irradiation optical path, and a light component inthe band of 570 to 600 nm is not used, the color purity can improve.Generally, however, when a light component that lowers the color purityis shielded, the light quantity decreases, although the color purityimproves. For the optical element 13, the cut band and transmittance areset such that the color purity and color balance can be ensured withoutgreatly decreasing the light quantity.

[0100] In the arrangement shown in FIG. 7, only the light component inthe green wavelength region changes its light quantity, as shown inFIGS. 9A and 9B. Hence, transparent glass is used as the substrates ofthe polarizing plates in the blue and red wavelength regions, cooling bya cooing fan is done mainly for the blue and red wavelength regions, andsapphire is used as the substrate of the polarizing plate in the greenwavelength region where the light quantity changes, the thermal load onthe polarizing plates in the respective wavelength regions can berelaxed. In addition, since the number of sapphire substrates decreases,the cost can be reduced.

[0101] Furthermore, since cooling by the cooling fan need only be mainlydone for the blue and red wavelength regions where the light quantitydoes not change, the power consumption and size of the fan can reduced,and the problem of noise is also relaxed. The spectral wavelengthcharacteristics of the dichroic mirror DM1 are not limited to thesecharacteristics. A plurality of optical elements may be used inaccordance with the characteristics.

[0102] Referring to FIG. 7, two sapphire substrates G1 and G2 are usedas the substrates of polarizing plates G1 and G2. However, the number ofsubstrates is not limited to two. In addition, not sapphire but anothermaterial such as fluorite having a high thermal conductivity may beused. Furthermore, as shown in FIG. 17, instead of using a substrate 100formed from a material such as sapphire or fluorite having a highthermal conductivity as the substrate of a polarizing plate, thesubstrate may be integrated with a display element. In this case,sapphire or fluorite can be used for both of the substrate of apolarizing plate and the display element or selectively used for only anoptimum one of the polarizing plate and display element.

[0103] [Third Embodiment]

[0104]FIG. 10 shows the detailed arrangement of a projection-typedisplay apparatus according to the third embodiment of the presentinvention. In the first and second embodiments, a plurality of liquidcrystal display elements are used. However, the present invention is notlimited to this, and color display can be realized using a single liquidcrystal display element. This will be described next as the thirdembodiment of the present invention. FIGS. 11A to 11D show the spectraltransmittances of dichroic mirrors DM4 to DM7 in the above arrangement.FIGS. 12 and 13 show, respectively, the outline of an optical path, andthe internal structure and optical paths in a liquid crystal displayelement according to this embodiment.

[0105] Light is separated into blue-, green-, and red-band lightcomponents by the dichroic mirrors DM4 to DM7 that exhibit the spectralreflectivities shown in FIGS. 11A to 11D, and a microlens array 14placed on the light source section side of the liquid crystal displayelement 8 is irradiated with the blue-, green-, and red-band lightcomponents at different incident angles. A liquid crystal layer 16 ofthe liquid crystal display element 8 is divided into pixelscorresponding to the blue-, green-, and red-band light components, asshown in FIG. 14, and these pixels are independently driven. The blue-,green-, and red-band light components pass through the microlens array14 and enters corresponding pixels such that the pixels are divisionallyirradiated with the light components in units of colors.

[0106] When the dichroic mirror DM6 having a spectral characteristicshown in FIG. 11C and the dichroic mirror DM7 having a spectralcharacteristic shown in FIG. 11D are replaced in the optical path,display with priority on the color reproducibility and display withpriority on the brightness are realized by a single apparatus. When thedichroic mirror DM6 is in the optical path, display with priority on thecolor reproducibility is performed without using a light component inthe band of 570 to 600 nm. When the dichroic mirror DM7 is in theoptical path, display with priority on the brightness is performed usinga light component in the band of 570 to 600 nm.

[0107] When sapphire substrates are used as the substrates of polarizingplates necessary before and after the liquid crystal display element,thermal load on the polarizing plates in display with priority on thebrightness is reduced, and the power consumption of a cooling fan isalso decreased. Instead of the dichroic mirror DM7, a typical metalmirror may be used.

[0108] As described above, when a mechanism for inserting and removingthe optical element is used, display qualities of two types can berealized. The insertion and removal of the optical element can be donemanually or by combining power generator and transmitter. In addition,when sapphire is used as the substrate of a polarizing plate, thermalload on the polarizing plate is relaxed.

[0109] Referring to FIG. 10, two sapphire substrates are used as thesubstrates of polarizing plates P1 and P2. However, the number ofsubstrates is not limited to two. In addition, not sapphire but anothermaterial such as fluorite having a high thermal conductivity may beused. Furthermore, as shown in FIG. 17, instead of using a substrate 100formed from a material such as sapphire or fluorite having a highthermal conductivity as the substrate of a polarizing plate, thesubstrate may be integrated with a display element. In this case,sapphire or fluorite can be used for both of the substrate of apolarizing plate and the display element or, a material having a highthermal conductivity such as sapphire, fluorite or the like may beselectively used for only an optimum portion of an element subject tothermal load such as the polarizing plate, display element or the like.

[0110] In the foregoing embodiments, sapphire or fluorite having a highthermal conductivity is used as a material for the substrate of thedisplay element or the polarizing plate for the sake of example. Suchmaterial having a high thermal conductivity, however, is not limited tosapphire or fluorite. Diamond or any other materials may be used as longas those material have a high thermal conductivity.

[0111] Further, the substrate of the polarizing plate or the substrataof the display element may be made from two kinds of materials or more.In this case, plate-like members of two or more kinds of materials maybe adhered together, or thin film of one material may be formed on aplate-like member of another material, or two or more kinds of materialsmay be mixed. On the other hand, in order to accomplish one of objectsof the invention that thermal load is reduced, it is preferable that atleast one of two or more kinds of materials has a thermal conductivityhaving 2 W/(m·k) or higher.

What is claimed is:
 1. A display apparatus for forming a color image byilluminating one or a plurality of display elements with light from alight source and modulating a plurality of color light components havingdifferent colors by the display elements, comprising: means for changinga color purity of at least one of the plurality of color lightcomponents; and a polarizing plate in an optical path of the lightcomponent whose color purity is changed by said color purity changingmeans, said polarizing plate having a transparent substrate including amaterial having a thermal conductivity higher than 2 W/(m·K).
 2. Anapparatus according to claim 1 , wherein said color purity changingmeans can adjust whether a light component in a specific wavelengthregion reaches the display element.
 3. An apparatus according to claim 2, wherein the light source has a peak at a certain wavelength of thespecific wavelength region.
 4. An apparatus according to claim 3 ,wherein the certain wavelength is 570 to 600 nm.
 5. An apparatusaccording to claim 4 , wherein the light source comprises ahigh-pressure mercury-vapor lamp, and the certain wavelength is about580 nm.
 6. An apparatus according to claim 2 , wherein said color puritychanging means comprises a dichroic mirror.
 7. An apparatus according toclaim 1 , wherein the transparent substrate is essentially made of oneof sapphire and fluorite.
 8. An apparatus according to claim 1 , whereinthe transparent substrate includes a material having a thermalconductivity higher than 5 W/(m·K).
 9. An apparatus according to claim 1, wherein the transparent substrate is essentially made of materialhaving a thermal conductivity higher than 2 W/(m·K).
 10. An apparatusaccording to claim 1 , further comprising a plurality of dichroicmirrors for separating white light from the light source into theplurality of color light components having different colors.
 11. Anapparatus according to claim 10 , further comprising a plurality ofimage elements arranged in correspondence with the plurality of colorlight components having different colors, and a plurality of dichroicmirrors for combining image light components from the plurality ofdisplay elements.
 12. An apparatus according to claim 10 , furthercomprising a plurality of display elements arranged in correspondencewith the plurality of color light components having different colors,and a dichroic prism for combining image light components from theplurality of display elements for modulating the plurality of colorlight components.
 13. An apparatus according to claim 12 , wherein saiddichroic prism is formed by bonding four prisms using an adhesive tohave wavelength selection/reflection layers substantially perpendicularto each other.
 14. An apparatus according to claim 1 , wherein saidcolor purity changing means inserts/removes an optical element to/froman optical path of at least one of the plurality of color lightcomponents or changes a posture of the optical element.
 15. A projectingapparatus comprising: said display apparatus of claim 1 ; and aprojection system for enlarging and projecting an image formed by saiddisplay apparatus.
 16. A display apparatus for forming a color image byilluminating one or a plurality of display elements with light from alight source and modulating a plurality of color light components havingdifferent colors by the display elements, comprising: means for changinga color purity of at least one of the plurality of color lightcomponents, wherein one of the one or plurality of display elements isin an optical path of the light component whose color purity is changedby said color purity changing means, said one display element having atransparent substrate essentially made of a material having a thermalconductivity higher than 2 W/(m·K).
 17. An apparatus according to claim16 , wherein said color purity changing means can adjust whether a lightcomponent in a specific wavelength region reaches the display element.18. An apparatus according to claim 17 , wherein the light source has apeak at a certain wavelength of the specific wavelength region.
 19. Anapparatus according to claim 18 , wherein the certain wavelength is 570to 600 nm.
 20. An apparatus according to claim 19 , wherein the lightsource comprises a high-pressure mercury-vapor lamp, and the certainwavelength is about 580 nm.
 21. An apparatus according to claim 17 ,wherein said color purity changing means comprises a dichroic mirror.22. An apparatus according to claim 16 , wherein the transparentsubstrate is essentially made of one of sapphire and fluorite.
 23. Anapparatus according to claim 16 , wherein the transparent substrateincludes a material having a thermal conductivity higher than 5 W/(m·K).24. An apparatus according to claim 16 , wherein the transparentsubstrate i s essentially made of a material having a thermalconductivity higher than 2 W/(m·K).
 25. An apparatus according to claim16 , further comprising a plurality of dichroic mirrors for separatingwhite light from the light source into the plurality of color lightcomponents having different colors.
 26. An apparatus according to claim16 , further comprising a plurality of image elements arranged incorrespondence with the plurality of color light components havingdifferent colors, and a plurality of dichroic mirrors for synthesizingimage light components from the plurality of display elements.
 27. Anapparatus according to claim 16 , further comprising a plurality ofdisplay elements arranged in correspondence with the plurality of colorlight components having different colors, and a dichroic prism forsynthesizing image light components from the plurality of displayelements for modulating the plurality of color light components.
 28. Anapparatus according to claim 16 , wherein said dichroic prism is formedby bonding four prisms using an adhesive to have wavelengthselection/reflection layers substantially perpendicular to each other.29. An apparatus according to claim 16 , wherein said color puritychanging means inserts/removes an optical element to/from an opticalpath of at least one of the plurality of color light components orchanges a posture of the optical element.
 30. A projecting apparatuscomprises: said display apparatus of claim 16 ; and a projection systemfor enlarging and projecting an image formed by said display apparatus.31. A display apparatus comprising: a light source; one or a pluralityof display elements illuminated with light from said light source, saiddisplay elements forming an image by modulating a plurality of colorlight components having different colors; and one or a plurality ofpolarizing plates arranged in an optical path of the light from saidlight source to equalize polarizing directions of the light components,at least one of said one or the plurality of polarizing plates having atransparent substrate essentially formed from a fluorite.
 32. Anapparatus according to claim 31 , further comprising means for changinga color purity of at least one of the plurality of color lightcomponents by inserting/removing an optical element to/from an opticalpath of said at least one color light component or changing a posture ofthe optical element in the optical path of said at least one color lightcomponent.
 33. An apparatus according to claim 32 , wherein said colorpurity changing means can adjust whether a light component in a specificwavelength region reaches the display element.
 34. An apparatusaccording to claim 33 , wherein the light source has a peak at a certainwavelength of the specific wavelength region.
 35. An apparatus accordingto claim 34 , wherein the certain wavelength is 570 to 600 nm.
 36. Anapparatus according to claim 33 , wherein the light source comprises ahigh-pressure mercury-vapor lamp, and the certain wavelength is about580 nm.
 37. An apparatus according to claim 31 , wherein said colorpurity changing means comprises a dichroic mirror.
 38. An apparatusaccording to claim 31 , wherein the transparent substrate includes amaterial having a thermal conductivity higher than 5 W/(m·K).
 39. Anapparatus according to claim 31 , wherein the transparent substrate isessentially made of a material having a thermal conductivity higher than2 W/(m·K).
 40. An apparatus according to claim 33 , further comprising aplurality of dichroic mirrors for separating white light from the lightsource into the plurality of color light components having differentcolors.
 41. An apparatus according to claim 40 , further comprising aplurality of image elements arranged in correspondence with theplurality of color light components having different colors, and aplurality of dichroic mirrors for combining image light components fromthe plurality of display elements.
 42. An apparatus according to claim40 , further comprising a plurality of display elements arranged incorrespondence with the plurality of color light components havingdifferent colors, and a dichroic prism for combining image lightcomponents from the plurality of display elements for modulating theplurality of color light components.
 43. An apparatus according to claim42 , wherein said dichroic prism is formed by bonding four prisms usingan adhesive to have wavelength selection/reflection layers substantiallyperpendicular to each other.
 44. A projecting apparatus comprising: saiddisplay apparatus of claim 31 ; and a projection system for enlargingand projecting an image formed by said display apparatus.
 45. A displayapparatus comprising: a light source; one or a plurality of displayelements illuminated with light from said light source, said displayelements forming an image by modulating a plurality of color lightcomponents having different colors, wherein at least one of said one orsaid plurality of display elements having a transparent substrate isessentially formed from a fluorite.
 46. An apparatus according to claim45 , further comprising means for changing a color purity of at leastone of the plurality of color light components by inserting/removing anoptical element to/from an optical path of the at least one color lightcomponent or changing a posture of the optical element in the opticalpath of the at least one color light component.
 47. An apparatusaccording to claim 46 , wherein said color purity changing means canadjust whether a light component in a specific wavelength region reachesthe display element.
 48. An apparatus according to claim 47 , whereinthe light source has a peak at a certain wavelength of the specificwavelength region.
 49. An apparatus according to claim 48 , wherein thecertain wavelength is 570 to 600 nm.
 50. An apparatus according to claim47 , wherein the light source comprises a high-pressure mercury-vaporlamp, and the certain wavelength is about 580 nm.
 51. An apparatusaccording to claim 45 , wherein said color purity changing meanscomprises a dichroic mirror.
 52. An apparatus according to claim 45 ,wherein the transparent substrate includes a material having a thermalconductivity higher than 5 W/(m·K).
 53. An apparatus according to claim45 , wherein the transparent substrate is essentially made of a materialhaving a thermal conductivity higher than 2 W/(m·K).
 54. An apparatusaccording to claim 47 , further comprising a plurality of dichroicmirrors for separating white light from the light source into theplurality of color light components having different colors.
 55. Anapparatus according to claim 54 , further comprising a plurality ofimage elements arranged in correspondence with the plurality of colorlight components having different colors, and a plurality of dichroicmirrors for combining image light components from t he plurality ofdisplay elements.
 56. An apparatus according to claim 54 , furthercomprising a plurality of display elements arranged in correspondencewith the plurality of color light components having different colors,and a dichroic prism for combining image light components from theplurality of display elements for modulating the plurality of colorlight components.
 57. An apparatus according to claim 56 , wherein saiddichroic prism is formed by bonding four prisms using an adhesive tohave wavelength selection/reflection layers substantially perpendicularto each other.
 58. A projecting apparatus comprising: said displayapparatus of claim 45 ; and a projection system for enlarging andprojecting an image formed by said display apparatus.
 59. A displayelement comprising: a transparent substrate essentially formed fromfluorite; and a driving section formed on said substrate.
 60. Apolarizing plate for equalizing polarizing directions of incident lightcomponents and outputting the light components, comprising: atransparent substrate essentially formed from fluorite: and a polarizingfilm formed on said substrate.